1. Field of the Invention
The present invention relates to an inkjet ink, an ink cartridge, and an inkjet recording device.
2. Description of the Related Art
Inkjet printers have advantages such as low noise, low running cost, and easiness of color printing, and thus have widely been used in ordinary homes as output devices of digital signals. In recent years, inkjet technologies have been utilized not only for home use but also for industrial applications such as displays, posters, and signboards. In such applications, porous media have problems with their durability such as light resistance, waterproofness, and wear resistance. Therefore, non-porous recording media such as plastic films have been used, and inks for them have been developed.
Such an inkjet ink (hereinafter may be referred to as “ink”) which has widely been used so far includes a solvent-based inkjet ink using an organic solvent as a vehicle, and an ultraviolet ray-curable inkjet ink containing a polymerizable monomer as a main ingredient.
The above solvent-based inkjet ink, however, gives off a large amount of solvent into air as a result of evaporation, which is not preferable from the viewpoint of environmental load. The ultraviolet ray-curable inkjet ink may be sensitive to the skin depending on the monomers used. In addition, use of the ultraviolet ray-curable inkjet ink requires incorporation of an expensive ultraviolet ray irradiation device into a printer main body, which limits its applicable fields.
Under such circumstances, developments have recently been made on aqueous inkjet recording inks which have low environmental load and have been used as inkjet inks for home use but which can directly print on non-porous base materials (see Japanese Patent Application Laid-Open (JP-A) Nos. 2005-220352 and 2011-94082).
However, several have been pointed out about the fact that these aqueous inks are inferior to solvent-based inkjet inks in terms of image quality.
First, an ink does not basically penetrate a non-porous base material and an ink on the base material has to be immediately dried. However, aqueous inks have downsides that their drying property is degraded due to water itself serving as a primary solvent of them and a water-soluble organic solvent added as an additive to easily cause drying failure. Therefore, when resultant printed matters are stacked on top of one another or rolled up, offset of the ink, so-called blocking, may disadvantageously occur.
Also, many non-porous base materials have very high gloss, and thus inks capable of providing high gloss have been required in order to ensure a sense of unity as a recorded matter between a printed portion and a non-printed portion formed after printing. In aqueous inks unlike solvent-based inks in which resins dissolves in inks, particles are fused to form a coating film and hence it is easier for the surface to be roughened to lead to degradation of its gloss. In addition, as for image robustness, satisfactory properties about scratch resistance, ethanol resistance, and light resistance have not yet been achieved, and higher performances have been required at present.
In particular, in outdoor applications such as advertisements and signboards among the aforementioned industrial applications, for example, high image robustness capable of passing JIS D0205 “Test Method of Weatherability for Automotive Parts” has been required at present.
As a measure to improve light resistance of an ink, an inkjet ink has been proposed in which a colorant is included in a polymer having in its molecular chain a moiety with ultraviolet absorbing property or light stabilizing property (see Japanese Patent (JP-B) No. 3446213).
This proposed ink, however, has a problem that it is degraded in drying property when used for non-porous recording media such as a plastic film, to thereby easily cause drying failure.
As a measure to improve scratch resistance of a printed matter obtained by applying an ink on a non-absorptive base material, an inkjet ink has been proposed which contains a polycarbonate group-containing polyurethane resin as a pigment dispersing agent in order to exhibit good storage stability (see Japanese Patent Application Laid-Open (JP-A) No. 2013-76018).
This proposal, however, uses the pigment dispersing agent as a resin for satisfying image robustness, especially scratch resistance, and an amount of the pigment dispersing agent added is also small, and as a result desired scratch resistance cannot be obtained. Note that, this proposal has descriptions that an ultraviolet absorber and a light stabilizer are used; however, they are not actually used in the Examples.
Under such circumstances, demand has arisen for provision of an inkjet ink that exhibits good drying property and provides a printed portion having a high level of gloss and being excellent in scratch resistance, ethanol resistance, offset resistance and light resistance when it is used for printing on a non-porous base material.